I have purchased a variety of accessories, so I decided to write about them below.

Hot shoe spirit levelThe 500D does not have a spirit level and if it did, the screen would have to be on anyway, so this comes in useful. I tend to use for landscapes, or when any form of camera support is used. I would say that is probably gets used about three times per a year, or something like that. They cost less than £10 to buy, and I would reccomend one.

UV FilterI purchased an inexpensive UV filter in an attempt to protect my kit lens, but later removed it. It degrades the image quality, and is not really worth using on a frequent basis.

Viewfinder CupI bought a viewfinder cup that is rubber and clips onto the camera's viewfinder. There are different versions available, but the one that I bought for £6 from ebay was utterly pointless. To keep my response short and polite, I will just say that it was nothing special, and actually made using the viewfinder worse.

LCD screen protectorThis is a piece of plastic that sticks over the screen. You may often find these going for like £20, but mine only cost £2 or so from ebay for a set. It works. It does get marked, but it prevents the screen from steaming up, and also protects it from scratches.

Lens HoodI have a lens hood for the kit lens, but not for my prime. This is really a personal preference, and I believe it makes no real difference for my use anyway.

Canon branded strapThis is included in the box with the camera. I used this for the first few months of ownership, but then founded that it was getting in the way and I had to coil it up all of the time to get the camera into the case. The 500D is only a plastic body anyway and the weight is manageable. I prefer to store my equipment in cases than having it dangling from my neck causing ache and risking potential damage to it. I would only use it now if I was photographing in areas where there is risk of dropping the camera, or similar.

Infra red remoteThis takes batteries and has to be pointed at the infra red on the front of the camera and is therefore a pain to use. I much prefer the wired option, see below. I would not reccomend this type of product.

Wired remoteThe wired shutter releases are great because they require no power, and just plug into the side of the camera. You can these for all prices from £1 upwards (mine cost £5 from ebay because of the build quality and branding), and extension cables are usually available, certainly for the mini jack type anyway.

Wireless flash triggersI use Yongnuo's which offer reasonable value for money and do what they say. I would reccomend this product.

Cleaning penThis one of those products with a pen shape body, where is there is a felt pad at one end and a retractable brush at the other. This tends to fall apart and there are better cleaning accesories. Although I use it, I would not reccomend it.

Useful: lens hoods & small neoprene bags to store them in,all for free thanks to Nikon; protector screen,also free from Nikon; neoprene neck strap,but only use in winter/autumn,because it makes you sweet like crazy;

Useless: Polarizer filters - sold,because they really decreased the sharpness & darkened the exposure by 3 stops. (which is killer for a variable aperture lens on a old CCD camera)
Also sold the battery grip,because it had no vertical AF control,which was pretty pointless,especially for portraits.

Lens hoods - agreed they should be used at all times. Also come free with purchase of any Sony lens.

Bulb blower - for sensor cleaning, this is approach #1, and usually handles 85% of all dust removal needs. Priceless.

DSLR sensor brush - for me, this is sensor cleaning #2 - gets another 10% of the stuff the bulb blower couldn't. Also priceless.

Wet swab sensor cleaning kit - cleaning #3 - for the ultimate stuff that won't come off via any other method - usually something you only need once a year or two, unless you frequent dusty, dirty places and change lenses a lot. I only use this when cleaning #1 and #2 fail to work.

Aftermarket strap - I hate the straps that come with cameras - nasty and uncomfortable especially for long lenses, so going with a nice wide neoprene strap to distribute the weight and remain comfortable even with much weight on it and sweating and hot. My Kata Reflex E strap has been aboard my last two cameras, and will continue to be on my next ones.

Wired remote relase cable - wireless remotes are cute and fun, but for me, I like having a power-free alternative that will work no matter what, powered by the camera itself, in case of any battery failures, signal issues, etc. There's something I'm just intrinsically more comfortable with for long exposure work, and a non-powered, wired remote is reliable and always works, and I feel much more comfortable with the ability to lock the shutter open and leave it that way for minutes at a time without thinking about dying batteries.

Tripod - gotta have one if you do long exposure work, which I do. Don't feel it necessary to go for 4-figure carbon fiber uber pods - aluminum works fine for me, I can handle the extra 1/2 pound of weight or so, and don't need any fancy heads since I only use it to set the camera up, point in the right direction, lock it down, and expose. A good $100-150 pod does just fine for me - free form legs, good 60" height, very compact and portable and fits in a bag or locker, reasonably light, well padded legs for carrying. Happy with my Slik Sprint Pro EZ for the past few years.

Filters - necessary? No, not for me. Fun? Sure. I get occasional use from a good circ polarizer, some ND filters, a UV/clear or two on certain lenses, and some specialty ones like a 9-stop ND which is fun for daytime long exposures.

Bags - lots of them, every size. Being a bit of a lens collector and having two bodies, I have to deal with an assembly of two cameras with about 20 lenses. So bags of varying sizes let me choose the bag for the occasion and the lenses needed. I have a small camcorder bag that accomodates my DSLR with attached superzoom and can squeeze one small prime too. I have a small shoulder bag that can accomodate DSLR and two lenses plus flash or mirrorless body alongside. I have a medium shoulder bag that can accomodate both cameras, plus up to around 4 lenses - or one camera, and up to 6 lenses. I have a two-lens holster bag that accomodates both of my long wildlife lenses side by side, allowing me to switch between the two lenses on the fly with my DSLR - the lenses point mount-up out of the bag, so I can insert the mounted lens into the empty holster, unlock from the body, move the body to the other lens, snap the camera body on, and slide it out of the other holster. And I have a large backpack that acts as transport, and accomodates the DSLR and 7 lenses - including the two big wildlife lenses mounted on body if needed.

Highly recommended, a small case for memory cards. Previously mine were in various pockets in my Tamrac and I was never sure which had recent images on and which were empty and formatted ready for shooting. A nice liitle case enables you to keep them separate and you always know where they are.

Undecided: CPL filter (impractical to use on lenses w/ a rotating front element but handy on those without)

Canon 500D wrote:

Infra red remote This takes batteries and has to be pointed at the infra red on the front of the camera and is therefore a pain to use. I much prefer the wired option, see below. I would not reccomend this type of product.

If I'm honest, I think you're missing the point of having and using an IR remote. If you're doing a self-portrait or a group photo where you are part of the group i.e. YOU are in front of the camera, the IR remote does have its benefits over the wired remote.

Canon 500D wrote:

Well, that depends on how frequently you use it, how heavy handed you are with your equipment, and how well you look after it. I have barely any marks on any of mine.

Even the most cautious person with meticulous care can be an unfortunate victim of circumstance, especially that which is beyond their control. I like to think I'm careful with my camera gear but I still maintain that prevention is better than the cure, which is why I still have a filter or hood attached to my lens.

Canon 500D wrote:

Memory Cards? I use one, which is kept in the camera.

How many do you need?

I don't think anybody can give a definitive answer to that question but yes, the one in your camera is the most important from a "here and now" perspective.

I have at least 5 memory cards altogether. One of them is specially reserved for video work as it has the write speed to cope and the others are for photos.

I have as many cards as I do for two reasons:

Damage limitation: a 64GB memory card, for the sake of argument, offers a huge amount of storage and convenience so you don't have to keep as many extra cards in case you run out of space. On the flipside, 64GB is also a huge amount of photos and videos to lose if the card is damaged, corrupted or misplaced. With eight 8GB or four 16GB memory cards, you can limit the loss more easily.

Emergencies: From my own experience, I think it makes sense to carry at least two cards - a few years back I was out in the countryside, at least an hour away from a photo/CE store, planning to do some photography only to find the card was corrupted, turning my camera into an expensive paperweight.

I generally don't feel the need for many memory cards, however I also agree on the idea of splitting up large amounts of memory onto several smaller cards rather than one big - security reasons alone, I like having things broken up to smaller bits, in case one fails I lose less.

As for my DSLR, I have two memory cards loaded in my camera so I can either use one for overflow if needed, or alternate between the two for shoots on two different days.